Extensive research has conventionally been made of tumors and tumor cells as a basis of development in an anticancer drug. As a result, it was found that solid tumors need oxygen and nutrients supplied through blood vessels for maintaining their homeostasis in vivo, and without such blood vessels, they cannot be grown to 2 mm or more in diameter in vivo [Basic Science of Cancer, authored by I. F. Tannock and R. P. Hill and translated by Naoyuki Taniguchi, Medical Science International (1993); and "Hatsugan to Gan Saibo" (Carcinogenesis and Cancer Cells)], Cancer Bioscience 3, edited by Toshio Kuroki, Tokyo University Press (1991)).
For this extension of blood vessels to solid tumors, it was proposed that solid tumor cells produce and secrete a certain factor (a tumor angiogenic factor) to induce blood vessels (J. Folkman, Annals of Surgery, Vol. 175, pp. 409-416 (1972)).
Attention has been paid to vascular endothelial growth factor as one of substances which functions as a tumor angiogenic factor (N. Ferrara et al., Endocrine Reviews, Vol. 3, No. 1, pp. 18-31 (1992)). Vascular endothelial growth factor is the same substance as so-called "vascular permeability factor", and in some cases it is also called "vascular endothelial growth factor/vascular permeability factor". As such factor, 4 kinds of molecular species, which occur due to the difference of splicing, are found in human.
Recently, it has been found that this vascular endothelial growth factor does not exert direct action (e.g. growth promotion) on solid tumor cells in experiments with cells (in vitro). However, it has been found that this factor promotes the growth of solid tumors in experiments with animals (in vivo). It has been further revealed that the growth of solid tumors is inhibited by administration of an anti-VEGF antibody to animals. These findings indicate that vascular endothelial growth factor is a tumor angiogenic factor (K. J. Kim et al., Nature, Vol. 362, April 29 issue, pp. 841-844 (1993); S. Kondo et al., Biochemical and Biophysical Research Communications, Vol. 194, No. 3, pp. 1234-1241 (1933)).
From the foregoing, inhibition of vascular endothelial growth factor leads to inhibition of growth of solid tumor cells, and this should be applicable in the development of anticancer agents. In fact there is a report on a method to use an anti-VEGF antibody. In this prior method, function of vascular endothelial growth factor (i.e. function of facilitating the growth of solid tumors) biosynthesized via translation of mRNA is inhibited by the anti-VEGF antibody.
However, this prior method is based on the assumption that vascular endothelial growth factor is present, therefore it is required for said factor not necessary to depress growth of tumor to be produced. Hence, this method cannot be effective until such substance is produced. Further, because vascular endothelial growth factor itself is biosynthesized without special inhibition, this method is problematic if the specificity and binding ability of the anti-VEGF antibody is poor and the inhibitory action of the antibody is incomplete.
Under these circumstances, there is proposed a method (referred to as antisense nucleic acid method) of using a nucleic acid compound (i.e. an antisense nucleic acid compound) which completely or almost completely inhibits expression of vascular endothelial growth factor itself by inhibiting production of vascular endothelial growth factors at the translation of mRNA, in place of inhibiting the action of vascular endothelial growth factor by use of said anti-VEGF antibody (Uchida et al., Antisense Res. & Dev., Vol. 5, No. 1, pp. 87-88, 1995; Nomura et al., J. Biol. Chem., Vol. 270, No. 47, pp. 28316-28324, 1995; WO 95/04142; WO 96/00286; WO 96/23065; WO 96/27006).
Whether the antisense nucleic acid method is effective or not depends on the method of selecting the antisense nucleic acid. That is, the method depends on how an effective nucleic acid compound completely or almost completely inhibiting production of vascular endothelial growth factor can be selected as the antisense nucleic acid compound. The present inventors have previously found and proposed antisense nucleic acid compounds which have nucleotide sequences complementary to the nucleotide sequence of the gene coding for vascular endothelial growth factor and which inhibit expression of vascular endothelial growth factor (International Publication WO 96/00286).